The research proposed here is designed to make critical contributions to a comprehensive clinical and experimental program focused on spatial cognition, and to set the stage for further inquiry into important questions about brain-behavior relations. These broad, long-term objectives are reflected in the specific aims of the proposal's two distinct studies. Study 1 aims to provide a carefully controlled lesion-based test of theories proposing that spatial cognition has its neural foundation in temporoparietal regions. It examines the performance of a control group and 3 patient groups (unilateral right hippocampal lesions, unilateral left hippocampal lesions, and parietal lobe lesions) on tasks of spatial cognition. Participants will be tested using a non-immersive desktop virtual environment task and related measures; these have been shown to provide valid and reliable tests of spatial learning, memory, and navigation. Structural neuroimaging and volumetric data will be available for all patients. Study 2 focuses on age-related changes in spatial cognition. It examines individual variability in performance on spatial tasks, asking questions like: Is high intra-individual variability in the performance of older adults on spatial tasks a behavioral indicator of compromised hippocampal functioning? The study will include 3 groups (healthy young adults, healthy older adults, and older adults with age-associated memory impairments). Participants will be tested across 15 occasions on the same apparatus used in Study 1. Extensive neuroanatomical data will be available for all older adults.